Many types of devices require that the rotational output of a common electrical motor, such as a stepper motor, be converted to a linear movement. One conventional rotational-to-linear movement is a leadscrew assembly. In a leadscrew assembly, a motor rotationally turns a leadscrew. A leadscrew follower engages the thread of the leadscrew to slidably move linearly along the length of the leadscrew according to the rotational direction and rotational velocity of the motor rotational output. A driven structure is affixed to the leadscrew follower.
The approach of the leadscrew assembly is widely used, but in some applications it has drawbacks. The axis of the leadscrew is parallel to, but transversely displaced from, the axis of movement of the driven structure, which can significantly increases the dimensions of the leadscrew assembly and can also lead to undesirable bending forces. The leadscrew assembly necessarily includes the mass and bulk of the leadscrew and the leadscrew follower, which are often much greater than the mass and bulk of the driven structure, so that the total mass and external dimensions may be much higher than that of the driven structure. For some applications, the added mass and size are highly undesirable. For those applications where the required axial travel of the driven structure is relatively short, the leadscrew assembly is operable but heavy and oversize. The leadscrew and follower are often made of a different material than the driven structure, so that there can be differential thermal stresses when the leadscrew assembly is heated or cooled.
There is accordingly a need for a different approach to converting the rotational motion of a conventional electrical motor to the linear motion needed for driving some driven structures, particularly those whose axial travel is relatively small. The present invention fulfills this need, and further provides related advantages.